Villalba-Galea Carlos A
Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia.
Biophys J. 2014 Oct 7;107(7):1564-72. doi: 10.1016/j.bpj.2014.08.017.
The voltage sensing domain (VSD) of the voltage-gated proton channel Hv1 mediates a H(+)-selective conductance that is coordinately controlled by the membrane potential (V) and the transmembrane pH gradient (ΔpH). Allosteric control of Hv1 channel opening by ΔpH (V-ΔpH coupling) is manifested by a characteristic shift of approximately 40 mV per ΔpH unit in the activation. To further understand the mechanism for V-ΔpH coupling in Hv1, H(+) current kinetics of activation and deactivation in excised membrane patches were analyzed as a function of the membrane potential and the pH in the intracellular side of the membrane (pHI). In this study, it is shown for the first time to our knowledge that the opening of Hv1 is preceded by a voltage-independent transition. A similar process has been proposed to constitute the step involving coupling between the voltage-sensing and pore domains in tetrameric voltage-gated channels. However, for Hv1, the VSD functions as both the voltage sensor and the conduction pathway, suggesting that the voltage independent transition is intrinsic to the voltage-sensing domain. Therefore, this article proposes that the underlying mechanism for the activation of Hv1 involves a process similar to VSD relaxation, a process previously described for voltage-gated channels and voltage-controlled enzymes. Finally, deactivation seemingly occurs as a strictly voltage dependent process, implying that the kinetic event leading to opening of the proton conductance are different than those involved in the closing. Thus, from this work it is proposed that Hv1 activity displays hysteresis.
电压门控质子通道Hv1的电压传感结构域（VSD）介导一种H⁺选择性电导，该电导由膜电位（V）和跨膜pH梯度（ΔpH）协同控制。ΔpH对Hv1通道开放的变构控制（V-ΔpH偶联）表现为激活过程中每ΔpH单位约40 mV的特征性偏移。为了进一步了解Hv1中V-ΔpH偶联的机制，分析了在膜片钳实验中切除的膜片上H⁺电流的激活和失活动力学，作为膜电位和膜内侧pH（pHI）的函数。据我们所知，本研究首次表明Hv1的开放之前存在一个电压非依赖性转变。有人提出类似的过程构成了四聚体电压门控通道中电压传感结构域和孔道结构域之间偶联的步骤。然而，对于Hv1，VSD同时作为电压传感器和传导通路，这表明电压非依赖性转变是电压传感结构域固有的。因此，本文提出Hv1激活的潜在机制涉及一个类似于VSD松弛的过程，这是一个先前在电压门控通道和电压控制酶中描述过的过程。最后，失活似乎是一个严格依赖电压的过程，这意味着导致质子电导开放的动力学事件与关闭过程中涉及的事件不同。因此，从这项工作中可以提出，Hv1活性表现出滞后现象。
